1. Field of the Invention
An aspect of the present invention relates to a platinum (Pt)/ruthenium (Ru) alloy catalyst, and more particularly, to a Pt/Ru alloy catalyst which is highly resistant to CO poisoning, thereby allowing for higher catalytic activity when used.
2. Description of the Related Art
A fuel cell is a power generating system which can directly convert energy generated in an electrochemical reaction of oxygen with hydrogen contained in a hydrocarbon-based material, such as methanol, ethanol, and natural gas, into electrical energy.
Fuel cells are classified into phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), polymer electrolyte membrane fuel cells (PEMFCs), and alkaline fuel cells (AFCs), etc., according to the type of electrolyte used. These fuel cells have basically the same operational principle, but differ from each other in the types of fuels, operational temperatures, catalysts, electrolytes, etc.
PEMFCs, which have been more recently developed, have greater power, can be operated at low operation temperatures, and have rapid starting and response characteristics. PEMFCs can be used for vehicles, houses and public buildings, electronic devices, etc.
In a membrane electrode assembly (MEA) of a PEMFC, a polymer electrolyte exists between an anode electrode and a cathode electrode. An oxidation reaction producing a hydrogen ion and an electron from the fuel occurs at the anode electrode, and the hydrogen ion produced is transported to the cathode electrode through the polymer electrolyte membrane. A reduction reaction producing water from the transported hydrogen ion and oxygen supplied from outside occurs at the cathode electrode.
In the PEMFC, hydrogen obtained by reforming gasoline, methane, methanol, etc., is used as a fuel. In the reforming reaction, hydrogen and a small amount of monoxide (CO) as a byproduct are formed. The catalyst is deteriorated due to the CO, and as a result, the performance of the PEMFC is deteriorated.
A direct methanol fuel cell (DMFC) is a PEMFC using methanol as a fuel. CO is formed as a byproduct of an oxidation reaction of the methanol at the anode and the catalyst is poisoned by the CO, and as a result, the performance of the DMFC is deteriorated.
A Pt/Ru alloy catalyst which is resistant to CO poisoning has been suggested. Japanese Laid-Open Patent Publication No. Hei 9-153366A describes a method of preparing a Pt/Ru alloy catalyst. In this method, a carrier, for example, carbon powders, is contacted with a solution of Pt and Ru cations to adsorb the cations on the carrier, and then the carrier is heated under reducing atmosphere to reduce the cations.
Noticing a relationship between the concentration of oxygen contained in a Pt/Ru alloy catalyst and resistance to CO poisoning, Japanese Laid-Open Patent Publication No. 2004-127814 describes a Pt/Ru alloy catalyst in which the concentration of oxygen is less than 4.4% by mass.
However, there is no mention that the resistance to CO poisoning can be obtained by using a Pt/Ru alloy having a uniform structure and a uniform distribution of particle size. Thus, there is a need to improve the resistance to CO poisoning of the Pt/Ru alloy catalyst.